In U.S. Pat. Nos. 2,923,813; 2,971,191; 3,007,164 and 3,066,293 the present inventor described several approaches to utilizing structures, such as automobile bodies, as transmitting or receiving antennas for radio waves. However, at the time of those inventions the present inventor was cognizant of the usability of only the boundary current flowing around the various discontinuities which are described in those patents, including discontinuities produced by the application of high-permeability ferrite materials over an area, as in FIG. 6a of U.S. Pat. No. 3,066,293. To stress this point once more, in the recited patents only currents flowing around an edge or boundary of a discontinuity in a conductive structure, e.g., a window in a vehicle, were utilized.
Only in recent experimentation was it discovered that by producing an impedance discontinuity in a region where currents were concentrated by reason of reduced cross section in the conductive body, as for example in a vertical column of a vehicle, a significant voltage drop could be produced across the current path impedance discontinuity, which voltage could be utilized very effectively to operate a radio receiver. The reciprocal phenomenon is also true, i.e., energy fed across such a discontinuity will be very effectively radiated by the conductive body. This use as a signal source or input of an impedance discontinuity in a region of reduced cross section, where body currents naturally are concentrated, rather than the boundary around a discontinuity, as previously taught, has been proved to produce a significantly more effective antenna system. To maximize the voltage drop across the impedance discontinuity and the coupling of energy into or out of the conductive body it is desirable to resonate, over the band of frequencies to be utilized, the inductive reactance appearing across the impedance discontinuity produced according to this invention.
While a single input or output region may be adequate for most applications, to minimize loss of signal because of directionality effects and to most nearly achieve omnidirectional-type performance, a plurality of separated regions of current concentration -- for example two rear columns in an automobile -- may be modified according to this invention to provide two space-phased antenna systems. Further, in the receiving mode, the voltage appearing across either or both of the current-flow discontinuities in the respective regions of current concentration can be "stepped up" by means of an auto-transformer preferably of the circuit configuration described in copending application Ser. No. 430,095 filed Jan. 2, 1974 by this inventor, although the configuration described in the previously recited patents may also be used.